The tilt angle is mechanically controlled for safety and is limited to around 15 to 20 degrees. To learn more about this style of window visit https://www.french-patiodoors.co.uk/upvc-tilt-and-turn-windows/
What are Tilt & Turn Windows?
Online Double Glazing Price Guides
Anyway, whichever reason they choose, you can find buyers guides here & there if you take look around on the web. We did just that ,and there is a decent one that we found right here: https://www.mylocalprices.co.uk/cost-guide/double-glazing-prices/